Hydrosere

plant succession

1. Plant Sucession Hydrosere Dr. Vasanta Kahalkar Assistant Professor Department of Botany M. G. Arts, Science & Late N. P. Commerce College, Armori

2. Plant Succession Definition :- Plant succession is an orderly change of communities of plant which occur over a period of time at the same place. Sere : - The stages in the communities that appear and disappear during course of succession are called sere and the communities area called seral communities or seral stages.

3. Causes of Successions Main causes of successions are follows :- (1) Physiographic processes :- Producing mostly primary bare area A) Erosion :- By wind, water, gravity or by glaciers. B) Deposition :- By water, wind and volcanoes. (2) Climatic phenomena :- Producing mostly secondary bare area. A) Wind :- Removing previous vegetation. B) Drought :- Death and wilting of weak species. C) Snow :- Killing previous vegetation D). Lighting :- Causes fire in the forest. (2) Biotic agents :- Producing mostly secondary bare area. A) Man :- Destroying natural vegetation B). Animals :- Overgrazing C) Bacteria, Fungi, insects :- Eliminating plant species by disease or by eating.

4. Hydrosere It is succession occurring in the aquatic environment. Hydrosere are well studied in ponds, lakes etc. Hydrosere , originated in a ponds start with the colonization of some phytoplanktons which form the pioneer plant community and finally terminates into a forest which is a climax community together with their chief component of vegetation. The plant succession which start in the aquatic environment is called hydrarch . A series of changes taking place in the vegetation of hydrarch is called hydrosere .

5. The process of aquatic succession completes in the following stages :- 1. Phytoplankton stage: In the initial stage of succession the simple forms of life like bacteria, algae and many other aquatic plants (phytoplankton) and animals (zooplankton) floating in water are the pioneer colonizers. All these organisms add large amount of organic matter and nutrients due to their various life activities and after their death, they settle at the bottom of pond to form a layer of muck.

6. 2. Rooted Submerged stage:- The phytoplankton stage is followed by submerged plant stage. When a loose layer of mud is formed on the bottom of the pond, some rooted submerged hydrophytes begin to appear on the new substratum. The submerged aquatic vegetation develops in the regions of ponds or lakes where water depth is about 10 feet or more. The pioneers are Hydrilla , Potamogeton , Myriophyllum , Ranunculus, Utricularia , Ceratophyllum , Vallisnena , Chara , etc. These plants bring about further build up of the substratum as a result of their death and decay. When these plants die their remains are deposited at the bottom of the ponds or lakes. The eroded soil particles and other transported materials are also deposited at the bottom. As this process of stratification progresses the body of water becomes more and more shallow, consequently the habitat becomes less suited for the submerged vegetation but more favourable for other plants.

7. 3. Rooted Floating stage: - When the depth of water reaches about 4 to 8 feet, the submerged vegetation starts disappearing from its original place and then the floating plants make their appearance gradually in that area. In the beginning the submerged and floating plants grow intermingled but in the course of time the submerged plants are replaced completely. The most tolerant species in the area are able to reproduce and perpetuate. Their broad leaves floating on the water surface check the penetration of light to deeper layer of water. This may be one of the main causes responsible for the death of submerged plants. Due to continuous interaction between plant communities and aquatic environment, the habitat becomes changed chemically as well as physically. More water and air borne soil and dead remains of plants are deposited at the bottom. Thus, the substratum rises up in vertical direction. Important floating plants that replace the submerged vegetation are Nelumbmm , Trapa , Pistia , Nymphaea , and Limnanthemum etc.

8. 4. Reed-swamp stages:- This stages is also known as amphibious stages as the plant of the community are rooted but most part of their shoot remain exposed to air. Species like of Scirpus , Typha , Phragmites etc are the chief plant of this stages. They have well developed rhizome and form a very dense vegetation. The water level is by now very much reduced and finally becomes unsuitable for the growth of these amphibious species.

9. 5. Sedge meadow stage Also called marsh meadow stage where the area is now made up of plant species like Carex (Sedge), Juncus , Diochanthium and herbs like Caltha , Polygonum , etc. They form a mat like vegetation with their much branched rhizomatous system. As result of high rate of transpiration, there is much rapid loss of water, & latter the mud is exposed to air as a result which the nutrient like ammonia, sulphides etc. become oxidized to nitrate and sulphates . Finally the marshy vegetation disappears due to the development of mesic conditions.

10. 6. Wood land stage:- By the time, of disappearnce marshy vegetation, soil become drier and drier for most time of the year. This area is now invaded by terrestrial plant. Which are some herbs, shrub & tree. By this time there is much accumulation of humus with rich flora of micro- prganism . Thus minerlization of the soil favours the arrival of new tree species in the area. 7. Forest stage :- It is the formation of climax community, which depends upon the climatic conditions. For e.g., tropical deciduous or monsoon forests are formed in regions of moderate rainfall, tropical rain forests in areas with heavy rainfall, mixed forests in temperate regions. Thus, in hydrosere stages 1 is pioneer community, stage 7 is climax community & 2-6 stage are seral community.

11. Diagram showing different plant community appearing different stages of a hydrosere in apond

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13. Xerosere : Dr. Vasanta Kahalkar Assistant Professor Department of Botany M. G. College, Armori

14. Xerosere : This is a type of xerosere originating on bare rock surfaces. The original substratum is deficient in water and lacks any organic matter, having only minerals in disintegrated unweathered state. The pioneers to colonise this primitive substratum are crustose type of lichens, and through a series of successive seral stages the succession finally terminates into a forest which constitutes the climax community.

15. Crustose lichens :- Stages In Xerosere Can Be Enumerated as Follows A bare rock consists of solid surface or very large boulders and there is no place for rooting plants to colonize. The crustose lichens like Licanora , Rhinodina can adhere to the surface of rock and absorb moisture from atmosphere. Therefore these colonize the bare surfaces of rocks fast. The Propagulis of these lichens are brought by air from the surrounding areas. These lichens produce acids which weathering the rocks. The dead organic matter of lichens becomes mixed with the small particle of rocks. However, this process is very slow. These lichens are then replaced by foliose and fruticose type of lichens .

16. Stage 2: Foliose and Fruitcose Lichen Stage Foliose have leaf like thalli while the fruticose lichens are small bushes. They are attached by the substratum at one point only. Therefore do not cover the soil completely. They can absorb and retain more water and are able to accumulate more dust particles. Their dead remains are decomposed to humus which mixes with soil particles and help building substratum and improving soil moisture contents further. The shallow depreciation in the rocks and crevices become filled with sold and top soil layers increases further. These autogenic changes favor growth and establishment of mosses. This community includes Permelia and Dermatpcarpom etc which have large leaf like thalli .

17. Stage 3: Moss Stage The development of thin soil layer on rock surface, especially in the crevices, favours the growth of some such xerophytic mosses as species of Polytricum , Tortula . At their successful growth they compete with the lichens. The bodies of mosses are rich in organic and inorganic compounds. When these die they add these compounds, to the soil to increase the fertility of the soil. The thickness of the soil layer now increases.

18. Stage 4: Herb Stage The thickness of the soil layer now increases. This changed habitat favors the growth of some herbaceous plant mostly annuals, in turn being followed by some biennial and perennial plant. Due to their growth and decay there is much more accumulation of humus in soil together with further weathering of rock. Thus, habitat changes with decreasing xeric condition. This stages is constituted by such shallow rooted grasses as Aristida , Poa etc. which in turn are replaced by shrubs.

19. Stage 5: Shrub Stage: Due to accumulation of soil the habitat becomes suitable for shrub species which start migrating in the area such as Rhus and others. They overshadow the harbaceous vegetation. The soil is further enriched by this dense shruby growth. These in turn are finally replace by trees which make up the climax community.

20. Stage 6:-Tree Stage Change in environment favors colonization of tree species. The tree saplings begin to grow among the shrubs and establish themselves. The kind of tree species inhabiting the area depends upon the nature of the soil. In poorly drained soils oaks establish themselves. The trees form canopy and shade the area. Shade loving shrubs continue to grow as secondary vegetation. Leaf litter and decaying roots weather the soil further and add humus to it making the habitat more favorable for growth to trees. Mosses and ferns make their appearance and fungi population grows abundantly.

21. Stages 7 : Forest stages or climax stages :- Some xerophytic tree species invade the area. Further weathering of rocks and increasing humus content of the soil favor the arrival of more trees and vegetation finally becomes mesophytic . Thus, there develop finally forest community.

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